The invention relates to a cleaning unit for removing the particles of developer which remains attached to the surface of an electrostatic latent image carrier used in an electrophotographic copying machine, an electrostatic recording system or the like.
A variety of cleaning units are known in the art which remove any residual particle of developer from a photosensitive member after an image transfer step. These typically include a fur brush cleaning, a blade cleaning, a roller cleaning, a magnetic brush cleaning and other techniques. A fur brush cleaning technique utilizes a hollow cylinder having a fur brush implanted on its surface and which is driven to rotate at a high speed for removing the toner from the photosensitive member. The toner deposited on the fur brush is removed by paddling the fur brush by means of a striker rod. The removed toner is conveyed by an air suction unit to be collected into a toner filter bag. Frequently, the technique is subject to a number of drawbacks including the dispersion of a toner from the casing of the cleaning unit to cause a contamination of surrounding parts, a degradation in the cleaning effect which occurs as a result of the bristles of the fur brush lying down after a prolonged period of use because of the increased length of the brush, and an increased size of the arrangement which is required. The blade cleaning technique utilizes a resilient blade having a relatively sharp edge as may be formed of polyurethane rubber and which is disposed in abutment against the surface of a photosensitive member. Hence, the surface of the photosensitive member is susceptible to damage. Once it is damaged, the image quality is greatly degraded, requiring a replacement of an expensive photosensitive member. When a photosensitive member is used which has an increased resistance to friction, the kind and arrangement of the photosensitive member is limited, resulting in the loss of flexibility in the design. In the roller cleaning technique, a resilient roller is used having a pliable layer which exhibits a resistivity not greater than 10.sup.8 ohm-cm. The roller is disposed in abutment against a photosensitive member to remove toner therefrom. However, if a magnetic carrier remains attached to the surface of the photosensitive member, the resilient roller is incapable of reliably removing it. In addition, there remains the likelihood that the photosensitive member may be damaged as with the blade cleaning technique. The magnetic brush cleaning technique, though it is little likely to damage the photosensitive member, has a reduced mechanical rubbing effect upon the surface of the photosensitive member, which prevents a satisfactory cleaning effect from being achieved. In addition, after a prolonged period of use, the toner concentration in the magnetic brush increases, resulting in a greatly reduced cleaning performance unless such toner is removed beforehand. It is also contemplated to use a cleaning roller comprising a sleeve on which bristles are implanted, but an increased number of revolutions of the sleeve causes an increase in the noise level from an associated drive motor and requires an increased torque. In addition, centrifugal effects causes the dispersion of the toner into the surrounding environment.
As discussed above, all of the described cleaning techniques are advantageous in some respect but are disadvantageous in others, and the prior art fails to provide an optimum cleaning technique. Thus it will be apparent that there is a need for a cleaning unit which is compact in construction while providing a high cleaning effect and avoiding a degradation in its performance with time and avoiding any damaging of a photosensitive member.